Deep brain stimulation (DBS) is a surgical treatment involving the implantation of a medical device, which sends electrical pulses to specific parts of the brain. The electrical pulses are delivered to the brain tissue by means of a probe having one or more electrodes, the probe being chronically implanted in the brain. DBS in selected brain regions has provided remarkable therapeutic benefits for otherwise treatment-resistant movement and affective disorders such as chronic pain, Parkinson's disease, tremor, dystonia and obsessive compulsive disorder. During DBS surgery, the most important step in determining the final implant position of a chronic DBS probe is test stimulation. Test stimulation is performed in order to both localize the optimal therapeutic target as well as to investigate the presence of side effect related structures surrounding the target. During test stimulation, a surgical team applies stimulation currents at various positions in and/or around the presumed target area and monitors the patient's response which may, e.g., be improvement (reduction) of disease symptoms and occurrence of (adverse) side effects. In dependence of the observed response, the surgical team configures the position of the probe controlling the stimulation process.
Test stimulation is often applied using an acutely implanted probe carrying a single macroscopic electrode suited for delivery of stimulation currents to the brain tissue. After having configured an optimal position, the acute probe is replaced by the chronic DBS probe. However, test stimulation may be applied also directly using the DBS probe that will be chronically implanted for therapy delivery, which has the advantage that positional errors due to electrode replacement may be avoided.
After a recovery period following the surgical procedure, the optimization of stimulation settings is started. For state-of-the-art chronic DBS probes only four electrodes, spaced apart by e.g. 2, 3, or 4 mm, are available. Currently, the optimization of stimulation settings follows essentially a procedure that is very similar to intra-operative test-stimulation (the procedure described above for the acute probe). To each of the electrodes carried by the chronic probe, stimulation is applied in a sequential order and a neurologist or nurse monitors the patient's response which may, e.g., be improvement (reduction) of disease symptoms and occurrence of (adverse) side effects. In dependence of the observed response, an optimum electrode—or an optimum combination of electrodes—of the chronic probe and stimulation settings are selected. Commonly, the electrode(s) providing lowest threshold for therapeutic effects and a large therapeutic window (i.e. high threshold for adverse-effects in relation to therapeutic threshold) is/are selected.
A preferred chronic DBS probe comprises a plurality of electrodes for providing stimulating electrical pulses at different positions in the target region. For example, the probe may comprise an array of 64 or 128 electrodes. For a simple DBS probe with one or only a few (e.g. four) stimulation electrode(s), the above described test stimulation process may be sufficient for locating the optimum electrode positions (intra-operatively) and/or for obtaining best stimulation settings (post-operatively). A physician or nurse provides one or more test pulses and observes and interprets the patient's physical and/or behavioral responses in order to select the optimum electrode position and/or optimum stimulation settings. However, for a DBS probe with a plurality of stimulation electrodes the known test stimulation process is far less suitable.
The plurality of stimulation electrodes allows accurate positioning of stimulation, e.g. by means of field steering techniques. Stimulation fields induced in the brain tissue and related patient responses are dependent on both the stimulus characteristics delivered to the selected individual electrodes and the resulting interactions between those stimuli. The time needed for testing of a representative number of possible parameter settings and electrode combinations for a DBS probe with a plurality of stimulation electrodes exceeds by far the practical time-frame available for this procedure in a clinical setting.
In view of the above, it is an object of the invention to make the above described determination of stimulation settings for a brain stimulation probe more time efficient.